Opportunistic infections are infections caused by pathogenic microorganisms that originally reside on the surface of the human epidermis, undamaged respiratory mucosa and digestive tract mucosa and cannot cause disease when the body’s immune function is normal, but overproliferate and invade the body when there is a decrease in resistance, destruction of the barrier function of the skin mucosa or impaired immune function. Opportunistic infections are not uncommon in daily life. Patients who have recently taken immunosuppressive drugs or whose body resistance has decreased due to illness, etc., are prone to opportunistic infections, such as bacterial diseases like tuberculosis and pneumonia, and fungal diseases like mycosis fungoides. In addition, AIDS patients are extremely susceptible to opportunistic infections. As a result of HIV infection, the most important CD4+ T lymphocytes in the human immune system are destroyed by a large number of attacks, which in turn leads to impaired immune function. At this time, some germs that are not pathogenic to normal people can invade and infect the body of AIDS patients, leading to illness or even death.